This application relates to the art of fluid pressure operated pilot control valves. The invention is particularly applicable to fluid control valves for appliances and will be described with particular reference thereto. It will be appreciated, however, that the invention has other applications in other areas where fluid flows are controlled.
Heretofore, pilot operated fluid valves have generally included a diaphragm assembly including a diaphragm connected with a diaphragm insert. Incoming fluid was received in a fluid inlet cavity to one side of the diaphragm and surrounding a valve seat. Fluid was discharged through a fluid outlet surrounded by the valve seat. A pilot reservoir was disposed on the other side of the diaphragm and insert from the inlet cavity connected with it by a pilot supply aperture and with the outlet by a pilot outlet aperture. A solenoid controlled, spring biased armature selectively opened and closed the pilot outlet aperture. When the pilot outlet aperture was opened, fluid flowed freely from the pilot reservoir allowing pressure in the fluid inlet cavity to lift the diaphagm from the valve seat. When the pilot outlet aperture was closed, fluid flowed into the pilot reservoir through the pilot supply aperture equalizing pressure on either side of the diaphragm allowing the armature bias spring, the diaphragm spring force, and the pressure differential across the valve seat to move the diaphragm against the valve seat.
In the past, the diaphragm had been integrally molded around the diaphragm insert. Such a molding operation required that the pilot supply apertures be relatively large. One problem with large pilot supply apertures was that suspended particles passed through them into the pilot reservoir where they caused the armature to hang up. Another problem with large pilot supply apertures was that they allowed fluid to pass into the pilot reservoir so fast that the valve closed very quickly causing high water hammer pressures. A further problem with large pilot supply apertures is that the pilot outlet aperture must be sized in relation to the pilot supply aperture. Specifically, the pressure force which must be overcome by the solenoid coil equals the area of the pilot outlet aperture times the maximum valve pressure differential. The pressure force must also be supported by the resilient seal without significant compression set because the seal may take radial excersions and will not always seal in the same place. Consequently, a larger pilot outlet aperture requires a larger annular support area to prevent compression set. The spring force must be proportional to the annular support area and, consequently, a higher spring force is needed. A correspondingly large and expensive solenoid coil was needed to move the armature against the spring force plus the pressure force.
One solution, which is illustrated in U.S. Pat. No. 3,593,957, issued July 20, 1971 to P. A. Dolter et al. and assigned to the assignee herein, was to replace the one piece molded diaphragm insert-diaphragm assembly with a separate plastic insert and diaphragm. In this arrangement, a single relatively small pilot supply aperture through the insert connected with a plurality of filtering apertures in the diaphragm. The applicant herein has found that one problem with the two-piece diaphragm insert-diaphragm assembly is that fluid flowing through the relatively large cross-sectional area of filtering apertures tends to bypass the insert pilot supply aperture by separating the diaphragm from the insert. This allows fluid to pass into the pilot reservoir so fast that the armature fails to remain seated against the pilot outlet aperture.
When the diaphragm and insert move toward the valve seat faster than the armature, the pilot outlet aperture is opened allowing the fluid pressure in the inlet cavity to lift the diaphragm away from the valve seat. Because the solenoid remains unactuated, the armature, after bouncing off the insert, again closes the pilot outlet aperture. The diaphragm and insert again move toward the valve seat faster than the armature which again opens the pilot valve outlet. This process is known as "chatter". The chatter continues until the energy is absorbed or damped out which may be an extended period of time. During the chatter, unwanted fluids continue to flow through the valve and out the fluid outlet. Various conditions tend to increase the tendency for chatter or the time to damp it out. These include the accumulation of air or gas in the pilot reservoir, connecting the valve with rigid plumbing, constructing the diaphragm of higher modulus rubber, utilizing a weaker solenoid and armature bias spring, and the like.
Another problem with the two-piece diaphragm insert and diaphragm assembly of the Dolter patent is that the diaphragm insert is relatively difficult and complex to mold. The diaphragm insert has an annular recess in its lower face for connecting the diaphragm filtering apertures with the pilot supply aperture and an annular recess around its valve seat aligning portion for anchoring the diaphragm. Because these two annular recesses extend in directions perpendicular to each other adjacent the same side of the insert, complex and multiple-piece die structures are required in order for the molded insert to be releasable from the mold. Such complex die structures are expensive to construct and difficult and time consuming to use.